US3055633A

US3055633A - Hot gas turbines

Info

Publication number: US3055633A
Application number: US728378A
Authority: US
Inventors: Pouit Robert
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-04-19
Filing date: 1958-04-14
Publication date: 1962-09-25
Anticipated expiration: 1979-09-25
Also published as: GB878367A; CH370596A; FR1245518A; DE1223623B; FR75183E

Description

p 1952 R; POUIT 3,055,633

HOT GAS TURBINES Filed April 14, 1958 3 Sheets-Sheet 1 INVENTOR 36 ROBERT POUIT iidw ATTORNEYS Sept. 25, 1962 R. POUlT HOT GAS TURBINES 3 Sheets-Sheet 2 Filed April 14, 1958 I (NVENTOR ROBERT POUIT" ATTORNEYS United States Patent Office 3,055,333 Patented Sept. 25, 1962 3,055,633 HGT GAS TURBINES Robert Pouit, 3 Rue Auguste-Mayet, Asnieres, France Filed Apr. 14, 1958, Ser. No. 728,378 Claims priority, application France Apr. 19, 1957 9 Claims. (Cl. 253-77) The present invention relates to turbines operated by a hot gaseous fluid which may result in particular from a vaporization or from a combustion.

The invention is more especially but not exclusively concerned with reaction turbines.

The chief object of my invention is to provide a turbine of the above mentioned kind which is better adapted to meet the requirements of practice than those known at the present time, in particular concerning the thermal and mechanical behaviour of their blades at the temperature existing during operation of the turbine.

For this purpose, according to my invention, the turbine rotor comprises, in combination, a wheel body including two adjacent discs, said discs having respective rim portions which form peripheral jaws and are provided with radial slots, a multiplicity of turbine blades, the root portions of said blades including inclined heels engaged under said disc jaws, a multiplicity of spacers interposed between said root portions of said blades, said blade root portions and said spacers being of complementary shapes, said spacers including inclined heels engaged under said disc jaws, and tightening means for keeping said discs applied against each other in the axial direction and at the same time resiliently holding said blade root portions and said spacers applied against one another in the circumferential direction.

Preferred embodiments of this invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example and in which:

FIG. l is a cross-section through a portion of the rim of a turbine rotor substantially on the line II of FIG. 3;

FIG. 2 is a similar cross-section on the line II-II of FIG, 3;

FIG. 3 is a developed plan view of the blades;

FIG. 4 is an enlarged view of the top portion of one of the blades in side elevation;

FIG. 5 is an enlarged view of a part of FIG. 3;

FIG. 6 is a cross-section through the rim of a modified form; and

FIG. 7 is a plan view of the blades of FIG. 6, partly in section.

The following description relates to the case of an axial turbine in which the degree of reaction is high and which is driven by a gas at high temperature.

The rotor of this turbine is constituted by a turbine wheel 1 supporting a plurality of blades 2 and this rotor is placed in a stator 3, where it is driven by a stream of hot gases indicated by arrows f (FIGS. 1 and 2). In the usual manner, the portion of each blade located upstream with respect to the stream of gas will be called front portion and that located downstream will be called rear portion.

It is known that the problem of protecting the blades against the action of heat is a difficult one. For this purpose it has already been proposed to protect the walls of the blades from the hot gases by films of blown air. It has also been proposed to deposit on the external surface of the blades a protective layer of a metal having a low thermal conductivity. In both cases, a cooling fluid such as air may also be circulated in the .blades so as to absorb the amounts of heat which have succeeded in penetrating thereinto. This cooling fluid may be constituted in the first case by the blown air itself and in the second case by air circulating through radial channels provided in the blades.

Furthermore, it is known that the protection of the blades by such films of air blown thereon is chiefly efl'icient when the air flows under laminar conditions. Unfortunately, such conditions are very unstable at the velocities of flow of the power gases (high Reynolds numbers) in the passages between the turbine blades. In order to stabilize such laminar flows, the expansion of the power gases in these passages must be made to take place with a degree of reaction sufficient to impart a high acceleration to the power gases flowing through said passages. However, due to the kinematic conditions which determine the shape of these passages, it is known that it is chiefly near the outlet of these passages that it is possible to achieve the high acceleration that is capable of stabilizing the laminar flow of the films of blown coolingair.

The turbine includes means for producing a laminar flow of cooling gas at high velocity, substantially parallel to the direction of flow of the power gases, along only the rear portion of the blades, that is to say where there is a high reaction, and consequently a high acceleration of the power gases, and other protection means are provided on the front portion of the blades. Advantageously, these last mentioned means are constituted by a sheet or jacket of a refractory material which is a bad conductor of heat, such as nickel or a nickel alloy containing for instance some amount of chromium. Preferably, this sheet is disposed at a small distance from the surface of the blades and cooling air is made to circulate at low speed in the interval. Advantageously, the edges of said sheet are arranged so as to limit, with the surface of the blade, a slot through which said cooling air escapes laterally and thus to produce the laminar gaseous flow intended to cool the rear portion of the blade.

Of course, a cooling fluid may also be made to flow through the inside of each blade, and the walls of said blade may be coated with a metallic layer adhering to the surface thereof and made of a material which is a bad conductor of heat.

In the embodiments of this invention illustrated by the drawings, blades 2 are made of a metal preferably having a high thermal conduction such as sintered aluminium or a sintered aluminium alloy. Said blades include root portions 4a and 4b engaged in

jaws

5a and 5b which, in the embodiment of FIGS. 1 to 5, are carried by two discs 1a and 1b assembled in any suitable manner, for instance by screws 6 cooperating with tubular nuts 6a, the whole of said discs 1a and 1b constituting the wheel body 1. The front portion of each blade is designated by 2a an the rear portion by 2b, this rear portion being connected with the root portion 4b by a flat wall 7 substantially at right angles to the radial generatrices 7a of blade 2.

Between the front portion 2a and the rear portion 2b of each blade, there is provided an interval 8 extending from the top of the blade. However, there is a root portion 2c common to both of these

portions

2a and 2b, with a hole 10 therein opening into interval 8.

The front portion 2a of each blade is surrounded by a sheet 11 the rear edges 11a and 11b of which are located slightly beyond the front part of the rear portion 2b of the blade. Between these edges and said blade rear portion, there is left a small interval for the distribution, on the walls of said rear portion, of laminar air films, the air of these films coming from interval 8 as wil be more fully explained hereinafter.

The front portion 2a of the blade, which is already protected both by a thin deposit 34 (FIG. 5) of a material which is a bad conductor of heat and by sheet 11 itself (also made of a material which is a bad conductor of heat) is further protected by thin sheets of air circulating between the wall of the front portion 2a and the inner wall of sheet 11.

For this purpose, I provide, in the body of the front portion of the blade, recesses such as 12, 13, 14, and 15 forming, with sheet 11, passages extending in the radial direction. Some of these recesses (13, 14) open radially and others (12, 15) laterally in the direction of flow of the power gases into a notch such as 12a provided in sheet 11. At least some of these recesses may have throttled portions such as 16 for adjusting the velocity of flow of the cooling air. Anyway the distance between the bottom of the recesses and the sheet and the velocity of the air flowing between these two elements are chosen in such manner that the flow is laminar.

Finally, I may provide, in each of the

portions

2a and 2b of the blades, radial channels such as 17 and 18 through which cooling air is made to flow so as to dissipate the heat which penetrates into the blades despite the above described precautions.

Advantageously, the cooling air of each blade is collected from an annular space 19 extending along the periphery of wheel body 1 and to which air is fed through radial channels 20 from a source under pressure, the air in said chamber 19 being further compressed by the action of the centrifugal force. From this chamber 19, air flows:

- Directly to channels 17 and 18;

To the edges 11a and 11b of sheet 11 through hole and interval 8;

To recess 14 through conduit 21;

To recess 13 through a channel 22 starting from channel 21;

To recess 12 through a channel 23 starting from channel 17;

To recess through a channel 24 starting from channel 21.

In the embodiment illustrated by FIGS. 1 and 2, it has been supposed that the radial expansion of the blades is limited by an .annular rim 25, made of a metal which does not expand much under the action of heat, this rim being kept in position by pins 26 carried by the blades, an annular spring 27 being interposed between the blades and the rim. In this case, it may be advantageous to give the base 26a of each of these pins 26 a shape identical to the cross section of the interval 8. It is thus possible instantaneously to perform, by insertion of said base 26a, thefixation of pin 26 and a fluidtight closing of interval 8 at its outer end. As visible on FIGS. 1 and 2, rim 25 and spring 27 are provided with holes 25a, 25b and 27a, 27b, 270 so as to permit evacuation of the cooling air. In the modification of FIG. 6, rim 25 bears against the ends of the blades on which it is tightly applied for instance by hooping at high temperature and, in order to permit the outflow of the cooling fluid which has flown through the channels 18 provided in the rear portion of the blades, said channels are arranged to open into the outer rear walls 35a of the blades through slots 35. The holes 25a are directed in such manner as to project, in the form of a whirling ring, into the annular space existing between the rotor and the stator, the cooling fluid which has flown through the channels 35b provided in the front portion of the blades.

Concerningnow the fixation of sheets 11 on blades 2, flat spacing piece, or spacer, closes the bottom of each passage through, which the power gases flow between the blades, the inner end 11d of sheet 11 is inserted between the root of the corresponding blade and the adjacent spacers, and the blades and the spacers are fixed to the wheel body 1 through means ensuring a mutual tightening of these elements in the circumferential direction so as to keep the sheet in position.

As shown by FIG. 3, spacers 28 are given a shape complementary of that of the blade roots, so that they fit between them. and form therewith an outer gas-tight wall for annular chamber 19. These spacers 28 include heels 29a and 29b of a cross-section identical to that of the heels 4a and 4b of the blades and the surfaces of contact between said heels and the

jaws

5a and 5b of the wheel body are inclined in such manner that the tightening effort exerted by screws 6 produces a centripetal thrust on the blade root portions and the spacers which tends to assemble them tightly against one another. The tight engagement is made possible by the fact that the distance (FIG. 2) between the ends 5' of the inclined faces of the jaws furthest from the central plane of the rotor is greater than the distance between the outer ends 4 of the heels.

In order to give the wheel body 1 some circumferential resilience, the peripheral portions of discs 1a and 1b are provided with radial slots 36 (FIGS. 1 and 2) which extend at least from the roots 5 of the jaws (FIG. 2) to the outer peripheries of the disc.

Thus sheets 11, subjected to the action of the centrifugal force, are held at their inner ends by being caught over most of the periphery thereof between the blade root portions and the spacers. Although the section of the root portions of the blades corresponds substantially to the section of said blades over at least most of the distance along which sheets 11 are applied, I may however provide on the roots of the blades local reinforcements 30 (FIG. 5 such that the spacers 28 fit against them, and fold sheet 11 at these places so as to have it held against the radial side of said reinforcement.

The upper portions of sheets 11 may be maintained on the blades by bent portions such as 11c (FIG. 5) engaged in recesses such as the outlets of conduits 17 and/or by pins 31, preferably resilient pins, for wedging small tongues cut from the sheets in suitable housings 31a.

It should be noted that the outer surfaces of spacers 28 may be protected by sheets 32 of a material which is a bad conductor of heat, such as nickel or a nickel alloy containing for instance some amount of chromium. These sheets 32 are engaged at the same time as

heels

29a and 2% by the

jaws

5a and 5b of discs 1a and 1b. Advantageously, these sheets 32 are bearing on marginal ribs 33 of the spacers (FIG. 1) so as to provide insulating air cushions between the external surfaces of spacers 28 and sheets 32.

According to the embodiment of FIGS. 6 and 7, instead of having

jaws

5a and 5b and slots 36 provided directly in discs 1a and 1b, they are provided in plates 37a and 37b fixed on discs in and 1b, as shown on the drawing, by means of the above mentioned screws 6 and nuts 6a,

jaws

5a and 5b belonging to the rim portions 38a and 38b of plates 37a and 37b.

Said rim portions 38a and 3812 are given such a volume and such an outwardly oifset shape that the centrifugal force, indicated by arrow F on FIG. 6, applied during r0 tation of the turbine to the masses constituted by the portions of the rim located between slots 36, is offset with respect to the section of metal connecting said masses with plates 37a and 37b, whereby there is created in said sections a bending torque due to the reaction exerted by heels 4a and 4b under the effect of the centrifugal force exerted on blades 2 and on spacers 28, so as to keep in operation at high temperature at least the same tight fixation of the blades as when the turbine is at rest in the cold state.

The same arrangement for automatic tightening also applies to theembodiment of FIGS. 1 to 5 which does not includes plates 37a and 37b. However, in the advantageous case when the blades and also the discs 1a and 1b that support them are made of a light alloy the mechanical characteristics of which deteriorate very quickly when the temperature rises, it seems preferable to have recourse to separate plates such as 37a and 37b made of special spring steel which is less responsive to variations under the effect of the temperature, these plates forming a thermal protection screen between the usual distributor of the turbine and the heels of the blades.

Furthermore, in the embodiment of FIGS. 6 and 7, a stream of cooling fluid is made to pass under sheets 32. For this purpose, said sheets, which cover both the root portions 9 of the blades and spacers 28, are folded a first time to be caught between heel 4a and jaw 5a, or heel 4b and jaw 5b, thus forming a chamber 39 along one side of the blades, and a second time to be caught between heel 4a or 4b, and the periphery of the corresponding disc 1a or 1b on which said heel is applied by the pressure exerted on the blades. 'In operation, under the action of the centrifugal force, plates 32 assume a convex shape which moves them apart from the outer wall of the blades root portions against which they are applied in the cold state. In order to circulate cooling fluid in the interval thus created, I provide in spacers 38 grooves 40 which may be placed in communication with the channels for the circulation of the cooling fluid as above described.

However, when the turbine is provided with means for supplying, on the upstream side of the wheel body 1, a cooling fluid, such means being represented on FIG. 5 by a fixed chamber 41 adapted to be fed with fluid under pressure and closed by labyrinth sealing means 42, the leaks through this labyrinth sealing means are used to circulate the cooling fluid through the above mentioned space. For this purpose, I provide in sheet 32, opposite chambers 39, inlet slots 43 and outlet slots 44. Thus the cooling fluid having flown past the labyrinth sealing means, which is driven and centrifugated by the outer wall of disc 1a penetrates into grooves 40 through inlet slots 43 and flows out from said grooves through outlet slots 44. In order to maintain a pressure difference between the upstream chamber and the downstream chamber into which

slots

43 and 44 open respectively, so as to ensure circulation through grooves 40, I may provide in disc 1b divergent channels 20 so as to re-circulate the fluid leaks which have already circulated under sheets 32.

I further provide a flange 46 fixed on at least one of the discs 1a and 1b to support the root portions 9 of the blades 2 and the spacers 28 with respect to said discs. Said flange 46 may be provided with projections 47 which serve to center and to drive the blades and spacers. The inner edges of sheets 11 may be folded on the root portions 9 of the blades and caught between said root portions and flange 46.

Turbine wheels obtained according to my invention have their blades efliciently protected against the heat of the power gases and said blades are always resiliently mounted without play on their support with a tension which may be either constant or increasing together with the speed of rotation, whatever he the difference of expansion, in operation, under different thermal conditions.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and eflicient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended Within the scope of the accompanying claims.

What I claim is:

1. In a hot gas turbine, a rotor which comprises, in combination, a wheel body including two adjacent discs of resilient material, said discs having respective rim portions provided with flanges which form peripheral jaws with inclined faces directed towards the axis and provided with radial slots extending at least from the roots of the jaws to the outer perimeter of the wheel, a plurality of turbine blades, the root portions of said blades including complementarily inclined heels engaged under the inclined faces of said disc jaws, a plurality of spacers interposed between said root portions of said blades, said blade root portions and said spacers being of complementary shapes at their juxtaposed sides, said spacers including complementarily inclined heels engaged under the inclined faces of said disc jaws, the distance between the ends of the inclined faces of the jaws furthest from the central plane of the rotor being greater than the distance between the outer ends of the heels, and tightening means operatively engaging the discs drawing said discs towards each other in the axial direction, thereby exerting an inward radial pressure on the blade and spacer roots for resiliently holding said blade root portions and said spacers applied firmly against one another in the circumferential direction.

2. A turbine rotor according to claim 1 in which said rim portions of said discs are integral therewith.

3. A turbine rotor according to claim 1 in which said discs include plates fixed thereto, said rim portions being integral with said plates.

4. A turbine rotor according to claim 1 further in cluding a sheet of a refractory material disposed at a short distance from at least a portion of each of said blades, the inner edge of said sheet being clamped between the root portion of said blade and the spacers adjoining it.

5. A turbine rotor according to claim 1 further including a sheet of a refractory material covering at least a portion of each of said blades, at a small distance therefrom, and means for circulating a cooling fluid through the space between said blade and said sheet.

6. A turbine rotor according to claim 5 in which said sheet covers only the front portion of said blade, whereby a laminar gaseous flow escaping from said space runs along the rear portion of said blade.

7. A turbine rotor according to claim 1 in which the portions of said discs located between said radial slots form masses resiliently carried by the disc bodies and having respective gravity centers such that the centrifugal force applied to each of said masses when the turbine is running applies the heel portions of said masses against the heels of said spacers and of said blade root portion.

8. A turbine rotor according to claim 1 further includ ing sheets of a refractory material covering the outer surfaces of said spacers at a small distance therefrom and caught between the jaws of said discs and the heels of said spacers.

9. A turbine rotor according to claim 1 further including sheets of a refractory material covering, at a small distance therefrom, the outer surfaces of said spacers and of the root portions of said blades, said sheets being caught between, on the one hand, the jaws of said discs and, on the other hand, the heels of said spacers and those of said blades.

References Cited in the file of this patent UNITED STATES PATENTS 768,597 Geisenhoner Aug. 30, 1904 905,487 Worsey Dec. 1, 1908 1,008,758 Warren Nov. 14, 1911 1,118,361 Lasche Nov. 24, 1914 1,178,452 London Apr. 4, 1916 1,362,074 Baumann Dec. 14, 1920 2,401,826 Halford June 11, 1946 2,501,038 Fransson Mar. 21, 1950 2,568,726 Franz Sept. 25, 1951 2,623,727 McLeod Dec. 30, 1952 2,696,364 Bartlett Dec. 7, 1954 2,780,435 Jackson Feb. 5, 1957 2,810,544 Schorner Oct. 22, 1957 2,828,940 Newcomb Apr. 1, 1958 FOREIGN PATENTS 124,821 Switzerland Mar. 1, 1928 172,769 Germany Dec. 16, 1904 554,119 Germany July 13, 1932